JPS5920972A - Dendrite inhibitor in zinc-bromine battery - Google Patents

Abstract

PURPOSE:To provide dendrite inhibitor enabling a battery to operate for longtime with the electrode surface kept smooth, by using a certain heterocyclic 4th class ammonium salt as the effective component. CONSTITUTION:Heterocyclic 4th class ammonium salt as indicated in the general formula, such as methylalkylpyrrolidiniumhalide, methylalkylmorpholiniumhalide, and methylalkylpiperidiniumhalide, was added to 100ml of electrolyte several mg to several hundred mg. While using a water solution of 3mol/l of zinc bromide as the electrolyte for the cathode, charging was carried out with the current density at 20, 40, 60 and 80mA/cm<2> and the charged quantity of electricity of 360mAh/cm<2>, with the result that electrodeposition of zinc on the cathode surface was extremely smooth. The result was highly remarkable with current density of 20-60mA/cm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dendrite inhibitor for preventing zinc deposited and grown on the cathode surface of a circulating electrolyte zinc-bromine secondary battery from becoming dendritic.

The basic structure of an electrolyte circulating type J zinc-bromine secondary battery is as shown in Fig. 1, in which 1 is an electrode, 2 is a separator (diaphragm), and 6 is an electric conductor made of plastic or the like. frame made of an insulating material, 4 catholyte common manifolds, 5 catholyte channel, 6 anolyte common manifold, 7 anolyte channel, 8 catholyte chamber, 9 anolyte chamber, 1
0 is a dendritic zinc precipitate (dendrite).

When charging the above-mentioned battery, mark ■ in the diagram.
Bromine is precipitated on the anode chamber side, which is indicated by O, and zinc is precipitated on the cathode chamber side, which is indicated by O.

In this case, the bromine deposited at the anode simply dissolves in the electrolyte and circulates, but the zinc deposited on the cathode surface does not necessarily remain smooth, but instead forms dendritic structures of various sizes. (hereinafter referred to as dendrites).

The formation process of dendrites on the cathode surface is generally considered to be as follows. In other words, the metallic zinc that precipitates on the cathode surface in the early stage of charging is not formed uniformly over the entire surface of the electrode, but is deposited in spots, so that at this point it has already formed the nucleus of a dendrite. Therefore, during the subsequent charging and punching, metallic zinc is preferentially electrodeposited on each of the spots-formed nuclei, and these finally become dendrites.

When dendrites grow on the cathode surface, the electric field concentrates there, increasing the growth rate of the dendrites and reducing the chance of contact between the cathode surface and fresh llj liquid, which not only reduces battery efficiency but also causes the dendrites to grow faster. Since dendrites are extremely brittle, they tend to separate from the electrodes under relatively slight stress, and the dendrite fragments that separate in this way clog the electrolyte circulation pipe and cause the pump drive to slow down.

Furthermore, if this dendrite continues to grow without detaching from the electrode, it may break the diaphragm, or if its growth progresses to an extreme level, it may come into direct contact with the anode surface and cause a short circuit. Eventually, the battery may be destroyed, and therefore, suppression of the main formation of dendrites is one of the extremely important requirements.

Due to the above requirements, various studies have been conducted on dendrite inhibitors, such as ionic or nonionic surfactants and galvanizing brighteners, but these should be improved in their bromine resistance. Therefore, it was not possible to maintain stable performance even after long-term cycle use, and the original effect of suppressing dendrites was still insufficient.

The present inventors conducted various studies in order to find a dendrite inhibitor that does not have the above-mentioned disadvantages, and as a result, they discovered a dendrite inhibitor that can be operated for a long period of time while ensuring the smoothness of the electrode surface. reached. .

That is, Kinmei is a heterocyclic quaternary compound having the following structure in the molecule.
A dendrite inhibitor for a zinc-bromine battery, characterized in that a class ammonium salt is used as an essential active ingredient. = SO4).

Examples of the heterocyclic quaternary ammonium salt represented by the above general formula include the following.

In either case, the alkyl group represented by the substituent Xt has 6 to 16 carbon atoms. Preferably 4-14. Particularly preferably, it is selected from the range of 6 to 12.

Also, among those represented by X, norogens are bromine and chlorine.

The amount of the complex quaternary ammonium salt used as described above is:
In both cases, the solubility decreases as the number of carbon atoms in R in the formula increases, but the effective amount is 100 m7 of electrolyte! Number ~ ~ number 1 inside
00~Excellent initial effect is exhibited just by its presence.

A 3 mol/L zinc bromide aqueous solution is used as the cathode electrolyte, and a saturated amount of, for example, methyl dodecylmorpholinium bromide is coexisting therein to give a current density of IW20+ 4.
0+ OOs 80 mA/c4+ Charging period 6
Charging was carried out under the conditions of 60 mAh/CJ, and the state of zinc electrodeposition on the cathode surface was extremely smooth, especially between 20 and 60 mAh.
Excellent results were obtained at a current density of tnA/al.

The metallic zinc state had a gentle bump-like shape and was mechanically highly stable.

The above-mentioned tendency is generally the same when other types of ammonium salts are used [7, and 40z++AAi
It was confirmed that good results were maintained even when cycle operation was continued, with one cycle consisting of 6 hours of charging and 6 hours of discharging.

EXAMPLES Hereinafter, the effects of the present invention will be specifically explained with reference to Examples.

Example 1 Methyldecylpyridinium bromide (I) was charged until the amount reached 240 mAh/t:rl, and the results shown in the table below were obtained.

The details in the table were determined based on the following criteria.

A: The electrode surface remains smooth.

B: Small protrusions are observed, but relatively smooth. C: The surface is uneven and dendrites are observed.

The charging capacity is 240mAh/ using the saturated one inside.
Charge until d, observe the condition of the cathode electrode surface,
The results shown in the table below were obtained. The evaluation method was similar to that of Example 1.

Example 6゜For the dendrite inhibitors I, ■, and ■ in Example 2, 30 mA was applied to each of the six samples having carbon numbers of 8 to 12.
/cr/l・6 hours charge/discharge cycle test 20-
”)°I went through multiple cycles, but in each case the lightning and extreme surface evaluations remained A'.

There was almost no difference in the electrodeposited surface due to the difference in carbon, but in the case of compound groups, the order was If > I > III.
■ showed the most excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a partial cross section of an electrolyte circulation type zinc-bromine secondary battery. 1...'R[, 2...Paseparator% 6...Frame, 4...Catholyte manifold, 5...Catholyte channel, 6...Anolyte manifold, 7.
...Anolyte channel, 78...Cathode chamber, 9...
・Anode room 10...Dendrite agent Mitsuro Kimura, patent attorney

Claims (1)

[Claims] A dendrite (R = 03 to 16) in a zinc-bromine battery, characterized in that a heterocyclic quaternary ammonium salt having a ten-member structure in the molecule is used as an essential active ingredient.
an alkyl group, X is a halogen atom or